Editing Uranium (section)

====Oxides====
{{See also|Uranium oxide}}
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| footer = [[Triuranium octoxide]] (left) and [[uranium dioxide]] (right) are the two most common uranium oxides.
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Calcined uranium yellowcake, as produced in many large mills, contains a distribution of uranium oxidation species in various forms ranging from most oxidized to least oxidized. Particles with short residence times in a calciner will generally be less oxidized than those with long retention times or particles recovered in the stack scrubber. Uranium content is usually referenced to {{chem|U|3|O|8}}, which dates to the days of the [[Manhattan Project]] when {{chem|U|3|O|8}} was used as an analytical chemistry reporting standard.<ref>{{Cite book |last1=Kloprogge |first1=J. Theo |last2=Ponce |first2=Concepcion P. |last3=Loomis |first3=Tom A. |title=The periodic table : nature's building blocks : an introduction to the naturally occurring elements, their origins and their uses |date=2021 |publisher=Elsevier |isbn=978-0-12-821538-8 |location=Amsterdam |pages=861–862 |oclc=1223058470}}</ref>

[[Phase (matter)|Phase relationships]] in the uranium-oxygen system are complex. The most important oxidation states of uranium are uranium(IV) and uranium(VI), and their two corresponding [[oxide]]s are, respectively, [[uranium dioxide]] ({{chem|UO|2}}) and [[uranium trioxide]] ({{chem|UO|3}}).{{sfn|Seaborg|1968|p=779}} Other [[uranium oxide]]s such as [[uranium monoxide]] (UO), [[diuranium pentoxide]] ({{chem|U|2|O|5}}), and [[uranium peroxide]] ({{chem|UO|4|·2H|2|O}}) also exist.

The most common forms of uranium oxide are [[triuranium octoxide]] ({{chem|U|3|O|8}}) and {{chem|UO|2}}.<ref name="ANL-Chem">{{cite web |title=Chemical Forms of Uranium |publisher=Argonne National Laboratory |url=http://web.ead.anl.gov/uranium/guide/ucompound/forms/index.cfm |access-date=18 February 2007 |archive-url=https://web.archive.org/web/20060922180607/http://web.ead.anl.gov/uranium/guide/ucompound/forms/index.cfm |archive-date=22 September 2006 |url-status=dead}}</ref> Both oxide forms are solids that have low solubility in water and are relatively stable over a wide range of environmental conditions. Triuranium octoxide is (depending on conditions) the most stable compound of uranium and is the form most commonly found in nature. Uranium dioxide is the form in which uranium is most commonly used as a nuclear reactor fuel.<ref name="ANL-Chem"/> At ambient temperatures, {{chem|UO|2}} will gradually convert to {{chem|U|3|O|8}}. Because of their stability, uranium oxides are generally considered the preferred chemical form for storage or disposal.<ref name="ANL-Chem"/>